If I wanted to prove that smoking causes heart issues, what are some confounding variables? Beware of Confounding Variables The object of an experiment is to prove that A causes B. a confounding variable is a variable that may inadvertently affect the outcome. Lifestyle and family history may also effect the heart.
Sampling Identify the population you want to study. (Who are you applying your findings to.) Get a sample that is representative of the population you want to study. GET A RANDOM SAMPLE. sample population
Random Sampling A sampling is used when you cannot study the entire population you want to consider.
Random Assignment Once you have a random sample, randomly assigning them into two groups rules out confounding variables. Experimental Group v. Control Group. Assigning participants to experimental (Breast-fed) and control (formula-fed) conditions by random assignment minimizes pre-existing differences between the two groups. Breast milk makes children smarter!
Random assignment is needed to accurately infer cause and effect relationships.
One, both, or neither? It is possible to have either random selection or random assignment but not the other in a study. For instance, if you do not randomly draw 100 students from JMB, but instead just take the first 100 on an alphabetical list, you do not have random selection. But you could still randomly assign this nonrandom sample to treatment versus control. Or, you could randomly select 100 students from JMB and then nonrandomly (haphazardly) assign them to treatment or control. Also, it's possible to have neither random selection nor random assignment. You might nonrandomly choose two classes to be in your study. (This is nonrandom selection.) Then, you could arbitrarily assign one to get the new educational program and the other to be the control. This is nonrandom (or nonequivalent) assignment.
What is a quasi-experiment? When the investigator has no control over the independent variable, but has power over how the dependent variable is measured. Membership in the treatment level is determined by conditions beyond the control of the experimenter. Used extensively in the social sciences and psychology. If the subjects have NOT been randomly assigned to the treatment condition, the experiment is a quasi- experiment. If comparing males v. females it is a quasi-experiment An example of a quasi-experimental design would be a study in which you examine the effects of smoking on respiratory functioning. You might have people who smoke 1 pack a day and 2 pack a day smokers, but you can't really assign them into these groups (is it ethical to make people who smoke 1 pack a day now smoke 2?) You would then run your study, but when you make conclusions, you can't make any cause and effect conclusions.
Hawthorne Effect But even the control group may experience changes. Just the fact that you know you are in an experiment can cause change. Whether the lights were brighter or dimmer, production went up in the Hawthorne electric plant.
Hawthorne Effect FOR EXAMPLE, if a school principal observes a classroom of students reacting politely and enthusiastically to a new student teacher, can he be sure that the students are behaving appropriately because the teacher is excellent?
Potential Researcher Problems: When an experimenter s expectations influences the outcome of the experiment. Belief that your society, group, or culture is superior to all others, or that all groups are like yours.
Potential Researcher Problem Solutions: BLIND OBSERVERS: Neutral people other than the researcher SINGLE-BLIND STUDY: Either the researcher or the subject do not know which group received the experimental treatment. DOUBLE-BLIND STUDY: The researchers and the subject do not know which group received the experimental treatment. PLACEBO: Inactive substance or fake treatment used as a control.
The Placebo Effect Refers to an improvement in symptoms as a result of medical treatment with an inactive substance or staged medical procedure. Placebos have helped alleviate pain, depression, anxiety, Parkinson s disease, inflammatory disorders and even cancer. Conscious Belief + subconscious associations = relief from symptoms Up to 58% of US physicians prescribe placebos, according to a study by the NIH. 62% believe prescribing placebos is ethical. Penn and Teller alternative medicine
The Placebo Effect sham surgery
Potential Participant Problems: When the sample of the population is not representative of the population at large. When individuals involved in an experiment act or respond in ways they believe correspond with what the researchers are looking for.
What is the: IV? DV? Control V? Potential Confounding V? A researcher was interested in the effects of reward on intrinsic motivation. Some children were told that they would be given a special award for drawing with magic markers (an activity they already enjoyed). Other children were simply asked to draw with the magic markers. One week later, the children were unobtrusively observed for how much time they spent drawing with the markers. The children who expected and received a reward for drawing with the markers were less likely to draw with them later.
What is the: IV? DV? Control V? Potential Confounding V? Within a classroom setting, subjects were asked to listen to a guest instructor. All subjects were given a description of the instructor. Some subjects read a description containing the phrase People who know him consider him to be a rather cold person..., while other people read a description where the word warm was substituted for the word cold (otherwise, the descriptions were identical). After the lecture, subjects were asked to rate the instructor. Subjects who were told the instructor was warm gave him more favorable ratings compared to subjects who were told that the instructor was cold.